Interferometric determination of broadband ELF wave phase velocity within a region of transverse auroral ion acceleration

Broadband electric field fluctuations with typical amplitudes of 10-20 mV/m peak-to-peak and frequencies from 0 Hz to 3 kHz (BE-ELF) were observed coincident with a region of less than or equal to 200 eV transverse H+ acceleration (TAI) near the poleward edge of the pre-midnight aurora. The coherence and phase velocity of the electric fields were measured using a interferometric antenna array over the frequency range of approximate to 100 Hz to 3 kHz. These electric field fluctuations were found to have the following characteristics: 1) incoherence perpendicular to the geomagnetic field, 2) coherence parallel to the the geomagnetic field, 3) parallel phase velocity (omega/k(parallel to)) of 30 - 35 km/s upwards, 4) 0 < \k(parallel to)/k(perpendicular to)\ < 0.32. We show that these properties are compatible with the emission being electrostatic H+ cyclotron (EHC) waves. We also discuss possible generation mechanisms for the waves, and their relationship to the TAI.